The present invention relates to an improved spool construction for a trimmer head used in flexible line rotary trimming devices used to trim grass, weeds and other vegetation. More particularly, the invention is directed to an improvement in the construction of trimmer head spools of the type disclosed in U.S. Pat. No. 7,797,839 that allow new cutting line to be wound thereon and worn or broken line to be removed and replaced without having to separate the spool from the trimmer head housing.
Trimmer heads used in flexible line rotary trimmers generally carry one or two lengths of flexible nylon cutting line wrapped about an interior spool with the ends of the line or lines projecting outwardly through opposed apertures in the side wall of the trimmer head. The head is threadably mounted on the end of an elongated shaft and rotated at a high velocity by a gas or electric motor so that the ends of the cutting line project radially from the head and sever weeds or other vegetation. When cutting line projecting from the head breaks off or becomes overly worn, it must be severed and fresh line extended from the spool through the line outlet eyelets in the side of the housing. Bump-feed type heads include a line feed-out mechanism which responds to a bump on the ground intentionally applied by the operator to feed out a measured length of fresh cutting line which is typically cut to the desired length by a knife blade projecting from a shield attached to the trimmer above the cutting head and spaced a predetermined distance from the perimeter of the trimmer head housing. Manual heads do not include any such line feed-out mechanism. The spool must be manually rotated relative to the housing to pay out additional cutting line. Automatic heads include a mechanism that detects a loss of mass in the cutting line projecting from the head during use and, without the need for any action by the operator, pay out additional lengths of line from the spool through the eyelets.
In each of these types of heads, the length or lengths of cutting line are typically wound onto the spool by hand. As most cutting heads employ a single length of line wrapped about a spool with the end portions projecting from opposed sides of the cutting head, care must be taken during the winding of the spool to avoid crossing or otherwise tangling of the two lines within the spool which interferes with the paying out of fresh line. This is particularly important in automatic and bump-feed heads where centrifugal force is utilized to pull the new lengths of line from the spool during use as the head is being bumped against the ground as any line tangle will interfere with the proper feeding of the line. Difficulty in properly loading the line on the spool is the most common complaint of home users of flexible line trimmers. It also is a time consuming task for the professional user.
In many of the prior art trimmer heads, it is necessary to separate the spool from the housing to wind the cutting line about the spool. Various channel configurations in and through the spool have been developed that enable the line to be fed onto the spool through the eyelets in the housing without having to first remove the spool from the housing. While those configurations do facilitate the loading of line onto the spool, they did not eliminate the need to remove the spool from the housing (known in the trade as splitting the head) in the event the cutting line breaks proximate the eyelet during use. Unfortunately, this is a frequent occurrence when the rapidly rotating line strikes a solid object such as a fence post. When such breakage occurs, the load pulling outwardly on the line during use is effectively eliminated and the line recoils, drawing the severed end of the line inwardly through the housing eyelet. Fresh line can no longer be paid out through the eyelets without first splitting the head to gain access to the spool in order to unwind fresh line from the spool and thread the fresh line through the eyelet in the housing.
The trimmer heads disclosed in U.S. Pat. No. 7,797,839, the contents of which are incorporated herein by reference as though fully set forth herein, enable the user to quickly, easily and uniformly wind lengths of cutting line onto the spool and to remove and reload line on the spool without having to split the head even in those instances where line breakage occurs proximate the housing eyelet during use. To provide such loading and unloading of the line, the trimmer head spool is provided with a line receptor channel that traverses the spool and has geometrically opposed open ends through which the cutting line can enter and exit the spool. At least a transverse portion of the channel that is intermediary of its opposed ends and preferably located proximate the bottom surface of the spool, is open and exposed such that the portion of the cutting line passing therethrough is accessible to the user when the spool is operatively connected to the trimmer head housing.
Winding of the cutting line onto the spool is achieved by first aligning the spool with the trimmer head housing to which it is operatively connected such that the opposed open ends of the line receptor channel are radially aligned with the eyelets and/or openings in the surrounding housing sidewall. In the preferred embodiments of the invention, an end portion of the line can be directed through one of the openings in the housing wall and into the aligned line receptor channel. The line passes through a portion of the spool and exits the channel adjacent one side of the open intermediary portion of the channel. The end portion of the line is then directed back into the receptor channel on the opposite side of the open intermediary portion thereof and is extended through the remainder of the channel in the spool and out the other aligned opening in the housing sidewall. The line is then pulled through the trimmer head until approximately half of the total length of the line is protruding from each side of the trimmer head with a central portion of the line being disposed in the open intermediary portion of the line receptor channel. Alternatively, the two extended end portions of the cutting line can be inserted into and directed through the portions of the receptor channel disposed on the opposite sides of the open intermediary portion thereof. Each end portion of the cutting line is then pulled through one of the opposed pairs of openings in the spool and housing wall until again, approximately half of the total length of line is protruding from each side of the trimmer head and a central portion of the line is positioned in the open intermediary portion of the line receptor channel. Subsequent rotation of the spool relative to the housing will wind the cutting line about the spool.
To provide an even winding and distribution of the protruding cutting line about the spool and prevent tangling within the spool during winding, a cam and cam follower mechanism is provided in the operative connection between the spool and housing to cause the spool to translate upwardly and downwardly with respect to the housing when the spool is gripped by the lower body portion of the spool and rotated in a given direction relative to the housing. This reciprocating movement of the rotating spool with respect to the housing provides for an even distribution of the cutting line about the spool as the line is wound thereon. To remove the line from the head, the user need only grip the exposed portion of the line in the open portion of the line receptor channel and pull that portion of the line in a direction away from the spool and substantially parallel to the axis of rotation of the spool, whereupon the line will simply unravel from the spool and separate from the head.
While the trimmer head that is the subject of U.S. Pat. No. 7,797,839 has greatly simplified line loading and replacement for the user, the line receptor channel in the trimmer head that traverses the spool requires a relatively complicated molding process and the exercise of substantial care during fabrication to provide a smooth continuous interior channel surface along the curvilinear portions thereof. The existing spools in which that channel is formed also are relatively heavy due to the amount of material employed in their fabrication and are subject to warpage and surface irregularities as a result of shrinkage during the cooling of the freshly molded spools due to large concentrations of material. The spool construction of the present invention retains all of the line loading and replacement benefits of the trimmer head disclosed in U.S. Pat. No. 7,797,839 while obviating the above discussed fabrication issues.